Pestilence, Nocturnus, Atheist

Most of this stuff is OOP, but can still be found fairly easily. Here are my recommendations:

Atheist-'Piece of Time'; 'Unquestionable Presence'
Nocturnus- 'The Key'; 'Thresholds
Pestilence- 'Malleus Maleficarum'; 'Consuming Impulse'

Those two Pestilence albums have (then) future Asphyx vocalist Martin Van Drunen. I highly recommend Asphyx.
 
Nocturnus - I don't know too much about them. They released "The Key" in 1991, and it's one of the first (probably not THE first..) death metal albums to incorporate keyboards. It's quite good. Lyrics are kinda science fiction based, vocals are very raspy.

Pestilence - I just bought "Testimony of the Ancients" and it kicks major ass. Very technical, yet still retaining memorable hooks and riffs. I don't know how it compares to their other albums, but from reading the other responses and the poll that was posted here a while back, you really couldn't go wrong with any of their albums.

Atheist - I've only heard a handful of songs from them. Pretty good if you like the death/jazz combination.
 
Nocturnus:

Definitely get The Key. Excellent technical death metal.

Pestilence:

First two are raw death/thrash while Testimony of the Ancients is good death/jazz and Spheres is even more jazzy but the jazz isn't very well included in the metal so it is kind of an awkward listen.

Atheist:

First two are good technical death/thrash with bits of jazz influences on Unquestionable Presence. Elements is more of an distorted jazz executed not that well. Sounds awkward too.

NP: The Wounded - Dark Moon Generation
 
Pestilence - Spheres. thats a great one nobody mentioned.

if you like those bands get into the best one out of that style:

CYNIC!!!!!!!!!!!!!!


JAH